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  • 1
    Electronic Resource
    Electronic Resource
    GABAergic inhibition shapes frequency tuning and modifies response properties in the auditory midbrain of the leopard frog (1999)
    Springer
    Journal of comparative physiology 185 (1999), S. 479-491 
    Details
    ISSN: 1432-1351
    Keywords: Key words Iontophoresis ; Inferior colliculus ; Amphibian ; Rana pipiens ; Bicuculline ; GABA ; AbbreviationsBIC bicuculline methiodide ; CF characteristic frequency ; DNLL dorsal nucleus of the lateral lemniscus ; eFTC excitatory frequency tuning curve ; GABAγ-amino butyric acid ; IC inferior colliculus ; iFTC inhibitory frequency tuning curve ; PB phasic burst ; PL-1 primary-like 1 ; PL-2 primary-like 2 ; PL-3 primary-like 3 ; PSTH post-stimulus time histogram ; SPL sound pressure level ; SRN superficial reticular nucleus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The functional role of GABAergic inhibition in shaping the frequency tuning of 96 neurons in the torus semicircularis of the leopard frog, Rana pipiens, was studied using microiontophoresis of the GABAA receptor antagonist, bicuculline methiodide. Bicuculline application abolished, or reduced in size, the inhibitory tuning curves of 72 neurons. In each case, there was a concommitant broadening of the excitatory tuning curve such that frequency-intensity combinations that were inhibitory under control conditions, became excitatory during disinhibition with bicuculline methiodide. These effects were observed irrespective of the excitatory tuning curve configuration prior to bicuculline methiodide application. Results indicate an important role for GABA-mediated inhibition in shaping the frequency selectivity of neurons in the torus semicircularis of the leopard frog. Bicuculline application also affected several other response properties of neurons in the leopard frog torus. Disinhibition with bicuculline methiodide increased both the spontaneous firing rate (18 cells) and stimulus-evoked discharge rate (81 cells) of torus neurons, decreased the minimum excitatory threshold for 18 cells, and altered the temporal discharge pattern of 47 neurons. Additional roles for GABAergic inhibition in monaural signal analysis are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003590050409
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  • 2
    Electronic Resource
    Electronic Resource
    A method for determining the unitary functional capacity of cloned channels and transporters expressed in Xenopus laevis oocytes (1995)
    Springer
    The journal of membrane biology 148 (1995), S. 65-78 
    Details
    ISSN: 1432-1424
    Keywords: Freeze-fracture ; Plasma membranes ; Heterologous expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The Xenopus laevis oocyte is widely used to express exogenous channels and transporters and is well suited for functional measurements including currents, electrolyte and nonelectrolyte fluxes, water permeability and even enzymatic activity. It is difficult, however, to transform functional measurements recorded in whole oocytes into the capacity of a single channel or transporter because their number often cannot be estimated accurately. We describe here a method of estimating the number of exogenously expressed channels and transporters inserted in the plasma membrane of oocytes. The method is based on the facts that the P (protoplasmic) face in water-injected control oocytes exhibit an extremely low density of endogenous particles (212±48 particles/μm2, mean, sd) and that exogenously expressed channels and transporters increased the density of particles (up to 5,000/μm2) only on the P face. The utility and generality of the method were demonstrated by estimating the “gating charge” per particle of the Na+/ glucose cotransporter (SGLT1) and a nonconducting mutant of the Shaker K+ channel proteins, and the single molecule water permeability of CHIP (Channel-like Intramembrane Protein) and MIP (Major Intrinsic Protein). We estimated a “gating charge” of ∼3.5 electronic charges for SGLT1 and ∼9 for the mutant Shaker K+ channel from the ratio of Q max to density of particles measured on the same oocytes. The “gating charges” were 3-fold larger than the “effective valences” calculated by fitting a Boltzmann equation to the same charge transfer data suggesting that the charge movement in the channel and cotransporter occur in several steps. Single molecule water permeabilities (p f s) of 1.4 × 10−14 cm3/ sec for CHIP and of 1.5 × 10−16 cm3/sec for MIP were estimated from the ratio of the whole-oocyte water permeability (P f ) to the density of particles. Therefore, MIP is a water transporter in oocytes, albeit ∼100-fold less effective than CHIP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234157
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    Paper (German National Licenses)
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